1. Field of the Invention
The present invention relates to electrohydraulic valves, and more particularly to such valves that control operation of intake and exhaust valves of a multi-cylinder internal combustion engine to selectively activate and deactivate or otherwise control operation of selected cylinders.
2. Description of the Related Art
In an effort to improve fuel economy, automobile manufacturers have devised systems that deactivate selected cylinders of an engine when the full power produced by all the cylinders is not required. For example, the “V-8-6-4 engine” is able to switch between four, six and eight cylinder operation. The selection of which cylinders to deactivate is determined by engine firing order with the desire to keep an even firing order in the deactivated mode. Several modes of cylinder deactivation are possible. In a bank mode, the multiple cylinders in the same bank of a V-configuration engine are switched at the same time, whereas each cylinder is switched independently in the cylinder control mode. A given cylinder is activated and deactivated by controlling the operation of the intake valves for that cylinder. By disabling the intake valve or valves for a given cylinder, the air-fuel mixture does not enter that cylinder and thus combustion does not occur. The exhaust valve also may be disabled in a similar manner.
The engine cylinder valve operation is controlled by a solenoid activated hydraulic valve which governs the flow of pressurized engine lubricating oil to a cylinder valve actuator. When the solenoid valve is energized, pressurized engine oil is applied from a workport of that valve to operate a spring-biased locking pin inside the cylinder valve lifter, which effectively decouples the cam shaft from the cylinder valve. When the solenoid is de-energized, the solenoid valve's workport is connected to the engine oil pan releasing the pressure at the cylinder valve actuator, which results in a spring biasing the locking pin to activate the intake or exhaust valve. Alternatively, the locking pin for the cylinder valve lifter can be configured so that energizing and de-energizing the solenoid valve has the opposite effects.
It is desirable to control the switching of the engine cylinder valves in less than one engine cycle. Therefore, the solenoid valve must respond very quickly in order to ensure timely deactivation and reactivation of the engine cylinder valve. Thus, it is desirable that the solenoid valve is required to generate as little force as possible thereby minimizing operating time.
When the engine is turned off, the lubricating oil that was used to control the engine cylinder valves drains into the oil pan and air enters the conduits of the valve control system. Therefore mechanism for bleeding the air from the system upon starting the engine has to be provided.
Because several solenoid activated hydraulic valves are require, it is desirable to provide a valve assembly which facilitates positioning and attaching those valves to the engine. In addition the valve assembly should be highly immune to vibrations, temperature changes and fluid exposure.